Large volumes of oil exist today in Canada and the United States trapped in deposits of sand or partially formed sandstone known as tar sand or oil sand, hereinafter referred to generically as tar sand. The tar sand is composed of sand, a heavy grade of hydrocarbon called bitumen, mineral rich clays, and water. Bitumen is a mixture of hydrocarbons that can be upgraded and refined by conventional hydrocarbon refining techniques into various consumer products such as gasoline, jet fuel, motor oil, asphalt and light gases such as ethane which can be converted to ethylene and ultimately polyethylene by conventional techniques. Separation of bitumen from the tar sand deposit traditionally has been difficult, costly and often not commercially viable. However, as conventional sources of oil are depleted, and the separation methods improve, tar sand deposits have been increasingly exploited. Nevertheless, separation remains difficult and costly, and methods of improving or easing the separation are needed.
One of the most common separation processes for removing the bitumen from the tar sand is the hot water extraction method. In this process, the tar sand is first removed from the ground using traditional mining techniques, normally strip mining. The mined tar sand is loaded into large vessels known as tumblers where it is combined with heated water or steam and often a caustic solution. The resulting tar sand water mixture is agitated to break apart any large chunks of the mined material and thereby form a relatively uniform slurry of water and tar sand. The physical action of mixing tar sand with the steam results in the separation of the tar sand mixture into two fractions. The first fraction, termed bitumen froth, rises to the top of the slurry mixture and is comprised mostly of bitumen, but also contains smaller amounts of water and solids. The second fraction, a water and solid fraction, settles to the bottom of the slurry and is a mixture of water, and solids. The type of solids found in tar sand may vary depending on the source of the tar sand, but often the solids comprise sand, clay, and other minerals that are mined along with the tar sand. Typically, the water and solid fraction is pumped to tailings ponds for later remediation. The bitumen froth, the fraction most heavily concentrated in bitumen of either of the fractions, is processed to remove more of the solids and water, before the bitumen is sent to be further refined.
The processing of the bitumen froth usually begins with the addition of a hydrocarbon diluent to the bitumen froth. The hydrocarbon diluent is added as a solvent to encourage settling of the water and solids. The resulting bitumen/diluent mix frequently contains greater than 10% water and 0.5% solids. The water in the bitumen/diluent mix contains salts, which can corrode processing vessels and equipment in later bitumen refining steps. To minimize corrosion and other problems, processors desire a reduced water and solid content.
Unfortunately, the water and solids in the bitumen/diluent mix form tiny droplets resulting in an emulsion. An emulsion is a system where tiny droplets of one liquid remain suspended in another liquid. In this emulsion, water droplets surround particles of clay, both of which are then suspended in the oil, and defy most conventional attempts to separate the droplets of water and clay from the bitumen and diluent. Gravity separators such as centrifuges are often used to encourage the separation of emulsions into a recoverable hydrocarbon fraction and a water/solid fraction. However, this step is expensive and often water and solids are still not separated from the bitumen/diluent mix to the extent desired. As a result of the retention of water at a higher than desired concentration, salts and clay contaminants in the recoverable hydrocarbon fraction cause processing problems and equipment damage in later refining steps that process the recoverable hydrocarbon fraction.